String Reversal using pointers

Question

Problem-To reverse a string using pointers, but my code instead of printing reversed string ,is printing the first letter of the string.

#include<stdio.h>

int main()
{
    int i;
    char n[100];
    char *ptr;
    ptr = n;
    char a[100];
    char *sptr;
    sptr = a;
    scanf("%s", n);

    for(i=0;n[i]!=0;i++)//Calculating the size of the string
        for(;(*sptr=*(ptr+i))!='\0';sptr++,ptr--)
        {
            ;
        }
    printf("%s",a);
    return 0;

}

"[c] string reversal" on this site will turn up a substantial number of hits. And no nested for loop is needed for this, so rethink your algorithm. — WhozCraig
– WhozCraig, Commented Feb 3, 2015 at 11:57
As it is you have a nested loop, i.e. the inner for loop which supposedly is meant to perform the reversal is nested within the loop calculating the string length. Is this intentional? — Frerich Raabe
– Frerich Raabe, Commented Feb 3, 2015 at 11:57
No it is not intended to be nested,my approach was to just calculate length of the string using it. — Beginner
– Beginner, Commented Feb 3, 2015 at 11:59
possible duplicate of Reverse a string using pointers in a function, output in main is garbled — 5gon12eder
– 5gon12eder, Commented Feb 3, 2015 at 12:01

Sourav Ghosh · Accepted Answer · 2015-02-03 12:29:15Z

1

Your problem is twofold.

First, you're missing a ; after the first for loop.

for(i=0;n[i]!=0;i++); //note the ;

Secondly, you're array index used is out-of-bounds

for(;(*sptr=*(ptr+i))!='\0';sptr++,ptr--)

you need to reduce i once before using it.

you should write

for(;(*sptr=*(ptr+i-1))!='\0';sptr++,ptr--)

Note: IMHO, you're making a simple thing too complex. Think of an easier logic. There are many. for a live example, follow the link in the comments by Mr. WhozCraig.

edited Feb 3, 2015 at 12:29

answered Feb 3, 2015 at 12:01

Sourav Ghosh

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1 Comment

WhozCraig Over a year ago

Or just do this and forget all the indexes. That's what the pointers are for.

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